Spica TC-50 loudspeaker Martin Colloms

Martin Colloms reviewed the Spica TC-50 in January 1988 (Vol.11 No.1):

The "transatlantic price penalty" means that a speaker appropriately priced according to performance for one market needs to be something rather special to survive the increase in price when exported to the other side of the Atlantic. One US miniature which has sold well in its home country is the Spica TC-50, now also available in the UK at a selling price of around £600/pair ($1000). Given the UK income level, this means that it rates as an expensive model over here, falling a little short of the legendary Celestion SL600. In the US, however, the Spica is almost a budget model, selling for a fraction of the price of the imported SL600! This means that any review for American readers must be quite differently oriented, in terms of value for money, from those which would pertain to the UK.

I call the Spica a miniature because that is what it is. Don't be misled by the fairly sized front panel, and instead follow my rule of thumb: models under 14 litres internal volume are miniatures. The Spica's volume is 11.5 liters. Admittedly it does look larger than this; the small volume is a function of the triangular side profile.

The TC-50 is a two-way design intended to provide good time alignment between the drivers, relying on a good, high stand to achieve this. For our auditioning, we used Cliff Stone's Foundation Pi models, with three-point alloy cone mounting to the Spica underside. These inert stands are lead/sand filled, and were well spiked to the floor.

In the main, this review covers the standard model, but we also had the opportunity of trying a higher-performance, more expensive version, upgraded here in the UK with Spica's permission. This improvement, in fact, adds £200 to the final selling price and is denoted by the "SE" suffix. It includes biwired terminals, special internal wire, panel damping, and a brace. These mods are not, however, available in the US.

Stereophile has reviewed the TC-50 before (AHC, Vol.7 No.2; JGH, Vol.9 No.5; AHC, Vol.9 No.7), and I shall not labor the appearance or background here. Heading straight into the technical description, the bass midrange is handled by a moderate-power-capacity 6.5" paper-cone driver built on a pressed-steel frame and equipped with a synthetic-rubber half-roll surround. Bass loading is sealed-box, and a 1" doped soft-fabric dome tweeter is used in the treble; both units are made by Audax in France. The tweeter is noted for its extended low range, which aids in the design of linear-phase, lower-order, crossover-slope filters. These are first-order, plus some corrective equalization applied to the out-of-band region of the midrange.

By sloping the front baffle steeply backward, the tweeter is brought into time alignment with the mid unit and both are then used off-axis, typically by 35 degrees. This improves the overall off-axis response and directs more energy than usual into the room, avoiding some of the minor peaks which often appear directly on-axis with drive units.

Sloping the baffle has other benefits as well: for example, it minimizes the symmetry of the side walls, thus reducing their panel-resonance contribution, while the anti-parallel internal shape also helps to break up internal acoustic standing waves.

The case is natural wood-veneered only on the two visible sides, with the rear and underside finished in satin black. The grill covers the full area of the front panel, and is made from a dark-brown woven polyester, the frame fitting neatly over an acoustic blanket, some 5/8" thick and made of soft felt, which covers the driver baffle. It is cut as an aperture for the bass-mid unit and as a horizontal slot, some 1¼" by 3", for the tweeter. Diffraction at the cabinet edges is thus reduced to a low value, while the directivity and power response of the tweeter are controlled by the slot geometry and its orientation. The usual energy step between the tweeter and the midrange unit may be reduced in this design due to the improved control of the tweeter's off-axis output.

The main case of the enclosure is of ¾" particle-board while the front baffle is made from MDF, the interior generously filled with cotton, said to be more effective than the usual Dacron wadding. In terms of mass being a factor in the internal absorption of enclosures, wool wins hands down.

Rear connections are made via a recessed terminal panel carrying two small 4mm socket/binding posts. This is rather cramped, preventing easy finger access to torque up the posts.

For the SE version, a second connector set is positioned next to the first, accepting the biwiring cable to the amplifier. In the SE, a brace is inserted, locking front and rear panels together to increase stiffness and to lower cabinet distortion (footnote 1). The reinforcement attaches to the boundary between the two drivers, a critical point. Bitumastic damping is also applied to the side walls, while the crossover remains untouched.

At present, there is no really convincing explanation as to why separation of the sections of a speaker in order to drive each with an individual cable should affect the sound as much as it does. Doing the same with multiple power amplifiers is also sonically rewarding; one might explain it as the reduction in broadband complex intermodulations in a piece of active electronics. By comparison, wire is so simple and electronically so linear that one is led to invoke ideas of ground impedance and crosstalk between the frequency sections of the speaker. The fact remains that biwiring is a valuable enhancement; we thus carried out separate listening sessions for the two versions of the speaker.

Sound Quality
Regardless of the SE mods, the essential character of the TC-50 remains, and first impressions of the standard speaker were of a clean-sounding, rather lightweight reproducer, with an explicit treble, good presence, much fine detail, and fine midrange transients.

It sounded even, in the sense that the more obvious bumps in the frequency range were absent, but there remained the effect of a gently rising response over the frequency range which ultimately robbed the cello region of its natural richness, and the bass of its full weight and scale.

Footnote 1: This brace is being incorporated in production TC-50s from December 1987.—John Atkinson
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